1. Field of the Invention
The present invention relates to the making of a composite profile comprising two metal members which are held apart from each other by means of at least two insulating bars, the edges of these bars being clamped in grooves formed between flanges on the metal members, by deforming at least the inner of the flanges which form these grooves. More specifically, the present invention relates to a method and a device for making such a composite profile.
2. The Prior Art
A composite profile of the type mentioned is disclosed in publicly accessible Norwegian patent application No. 76.4017. This application discloses the making of such a profile by placing the metal members (extruded profiles) and the insulating bars in mutually correct positions, and then forcing a mandrel lengthwise through the hollow space defined by the metal members and the insulating bars to cause the inner flanges in the metal members to be deformed into grooves running longitudinally along the insulating bars.
This prior art method, however, requires that the metal members be properly fixed relatively to each other during the joining operation. The finished composite profiles of the kind in question are suited for use for instance as sills and frames for doors and windows, and the dimensions of the profiles must lie within small tolerances, both on account of the appearance and because the profiles are to be joined in corners.
The purpose of using insulating bars is of course to reduce the heat transfer compared with profiles which consist entirely of metal, usually an aluminum alloy. The insulating bars, which may be made from a suitable plastic material, or bakelite rubber, have a low heat conductivity. However, the problem of achieving a low heat transfer in the transverse direction of the profile is not solved solely by a low heat conductivity in the material or materials of the profile, because convection in the air inside the profile and radiation inside the profile also play important roles.
It is well known that well reflecting surfaces inside such profiles cause a small heat transfer by radiation and that dark and dull surfaces cause a large heart transfer by radiation.
A main object of the present invention is to solve the above-mentioned problems relating to the dimension tolerances and the shape accuracy.
A further object is to take advantage of the known facts about radiation and thereby to achieve a reduced heat transfer.
Experiments have shown that anodizing has a considerable influence on the heat transfer by radiation. Thus, it is advantageous that the inner surfaces in the composite profile are not anodized. Calculations show that it is possible to achieve a reduction of the total heat transfer in the transverse direction of the profile, i.e., along the width of the insulating bars, of about 17% by use of un-anodized surfaces, compared with anodized surfaces. It is, however, necessary that the metal profiles are anodized on the outer surfaces, and the problem to be solved is how to avoid anodizing of the inner surfaces while anodizing the outer surfaces.
It is well known that profiles which are immersed in an anodizing bath will only be anodized on surfaces which are not shielded by other walls of the profile. Thus, hollow profiles (having walls which define a space which is only open from the ends of the profile) will mainly be anodized only exteriorly, the inner surfaces being anodized only a very short distance from each end of the profile.
Metal profiles which form parts of the composite profile shown in the Norwegian patent application No. 76.4017 will be anodized also on those surfaces which face into the hollow space formed by the succeeding insertion of the insulating bars. There are two possible ways to avoid this anodizing of the inner surfaces, namely to apply a coating to avoid anodizing or to carry out the anodizing after the insertion of the insulating bars.
None of these methods are desirable, the first because it increases the cost of manufacture and the second because it presupposes that the insulating bars withstand the immersion in the anodizing bath.
The present invention brings about the possibility to avoid these undesirable methods and still to achieve a low rate of heat transfer.